Consequence of altered nitrogen cycles in the coupled human and ecological system under changing climate: The need for long-term and site-based research

Anthropogenically derived nitrogen (N) has a central role in global environmental changes, including climate change, biodiversity loss, air pollution, greenhouse gas emission, water pollution, as well as food production and human health. Current understanding of the biogeochemical processes that govern the N cycle in coupled human–ecological systems around the globe is drawn largely from the long-term ecological monitoring and experimental studies. Here, we review spatial and temporal patterns and trends in reactive N emissions, and the interactions between N and other important elements that dictate their delivery from terrestrial to aquatic ecosystems, and the impacts of N on biodiversity and human society. Integrated international and long-term collaborative studies covering research gaps will reduce uncertainties and promote further understanding of the nitrogen cycle in various ecosystems.     

The challenge of making ozone risk assessment for forest trees more mechanistic

Upcoming decades will experience increasing atmospheric CO₂ and likely enhanced O₃ exposure which represents a risk for the carbon sink strength of forests, so that the need for cause-effect related O₃ risk assessment increases. Although assessment will gain in reliability on an O₃ uptake basis, risk is co-determined by the effective dose, i.e. the plant's sensitivity per O₃ uptake. Recent progress in research on the molecular and metabolic control of the effective O₃ dose is reported along with advances in empirically assessing O₃ uptake at the whole-tree and stand level. Knowledge on both O₃ uptake and effective dose (measures of stress avoidance and tolerance, respectively) needs to be understood mechanistically and linked as a pre-requisite before practical use of process-based O₃ risk assessment can be implemented. To this end, perspectives are derived for validating and promoting new O₃ flux-based modelling tools.     

Impact of biochar application to a Mediterranean wheat crop on soil microbial activity and greenhouse gas fluxes

Biochar has been recently proposed as a management strategy to improve crop productivity and global warming mitigation. However, the effect of such approach on soil greenhouse gas fluxes is highly uncertain and few data from field experiments are available. In a field trial, cultivated with wheat, biochar was added to the soil (3 or 6 kg m⁻²) in two growing seasons (2008/2009 and 2009/2010) so to monitor the effect of treatments on microbial parameters 3 months and 14 months after char addition. N₂O, CH₄ and CO₂ fluxes were measured in the field during the first year after char addition. Biochar incorporation into the soil increased soil pH (from 5.2 to 6.7) and the rates of net N mineralization, soil microbial respiration and denitrification activity in the first 3 months, but after 14 months treated and control plots did not differ significantly. No changes in total microbial biomass and net nitrification rate were observed. In char treated plots, soil N₂O fluxes were from 26% to 79% lower than N₂O fluxes in control plots, excluding four sampling dates after the last fertilization with urea, when N₂O emissions were higher in char treated plots. However, due to the high spatial variability, the observed differences were rarely significant. No significant differences of CH₄ fluxes and field soil respiration were observed among different treatments, with just few exceptions. Overall the char treatments showed a minimal impact on microbial parameters and GHG fluxes over the first 14 months after biochar incorporation.     

Developing spatially stratified N(2)O emission factors for Europe

We investigate the possibility to replace the – so-called – Tier 1 IPCC approach to estimate soil N₂O emissions with stratified emissions factors that take into account both N-input and the spatial variability of the environmental conditions within the countries of the European Union, using the DNDC-Europe model. Spatial variability in model simulations is high and corresponds to the variability reported in literature for field data. Our results indicate that (a) much of the observed variability in N₂O fluxes reflects the response of soils to external conditions, (b) it is likely that national inventories tend to overestimate the uncertainties in their estimated direct N₂O emissions from arable soils; (c) on average over Europe, the fertilizer-induced emissions (FIE) coincide with the IPCC factors, but they display large spatial variations. Therefore, at scales of individual countries or smaller, a stratified approach considering fertilizer type, soil characteristics and climatic parameters is preferable.     

N2O emissions from municipal solid waste landfills with selected infertile cover soils and leachate subsurface irrigation

This study presents the field investigations into the effects of cover soils and leachate subsurface irrigation on N₂O emissions from municipal solid waste landfills. Landfill Site A and Site B, covered with carefully chosen infertile soils, were selected to monitor their diurnal and seasonal variations of N₂O emissions. The annual average N₂O flux was 469 ± 796 μg N₂O-N m⁻² h⁻¹ in Site B with leachate subsurface irrigation, three times that of Site A without leachate irrigation. When an additional soil containing lower contents of carbon and nitrogen was introduced to cover part of Site B, its N₂O fluxes decreased by 1-2 orders of magnitude compared with the left area of Site B. This suggested that carefully selected cover soils could substantially reduce N₂O emissions even under leachate subsurface irrigation. Statistical analysis proved that the availabilities of soil moisture and mineralized nitrogen were the key parameters controlling landfill N₂O emissions.     

Processes and factors controlling N₂O production in an intensively managed low carbon calcareous soil under sub-humid monsoon conditions

An automated system for continuous measurement of N₂O fluxes on an hourly basis was employed to study N₂O emissions in an intensively managed low carbon calcareous soil under sub-humid temperate monsoon conditions. N₂O emissions occurred mainly within two weeks of application of NH₄⁺-based fertilizer and total N₂O emissions in wheat (average 0.35 or 0.21 kg N ha⁻¹ season⁻¹) and maize (average 1.47 or 0.49 kg N ha⁻¹ season⁻¹) under conventional and optimum N fertilization (300 and 50-122 kg N ha⁻¹, respectively) were lower than previously reported from low frequency measurements. Results from closed static chamber showed that N₂O was produced mainly from nitrification of NH₄⁺-based fertilizer, with little denitrification occurring due to limited readily oxidizable carbon and low soil moisture despite consistently high soil nitrate-N concentrations. Significant reductions in N₂O emissions can be achieved by optimizing fertilizer N rates, using nitrification inhibitors, or changing from NH₄⁺- to NO₃^ˉ-based fertilizers.     

Spectral estimation of global levels of atmospheric pollutants

Underlying levels of atmospheric pollutants, assumed to be governed by smoothing mechanisms due to atmospheric dispersion, can be estimated from global emissions source databases on greenhouse gases and ozone-depleting compounds. However, spatial data may be contaminated with noise or even missing or zero-valued at many locations. Therefore, a problem that arises is how to extract the underlying smooth levels. This paper sets out a structural spatial model that assumes data evolve across a global grid constrained by second-order smoothing restrictions. The frequency-domain approach is particularly suitable for global datasets, reduces the computational burden associated with two-dimensional models and avoids cumbersome zero-inflated skewed distributions. Confidence intervals of the underlying levels are also obtained. An application to the estimation of global levels of atmospheric pollutants from anthropogenic emissions illustrates the technique which may also be useful in the analysis of other environmental datasets of similar characteristics.     

Nitrous oxide and methane emission from a flooded rice field as influenced by separate and combined application of herbicides bensulfuron methyl and pretilachlor

Combination of divergent active principles to achieve broad-spectrum control is gaining popularity to manage the weed menace in intensive agriculture. However, such application could have non-target impacts on the soil processes affecting soil ecology and environmental interactions. A field experiment was conducted to investigate the impact of separate and combined applications of herbicides bensulfuron methyl and pretilachlor on the emission of N₂O and CH₄, and related soil and microbial parameters in a flooded alluvial field planted to rice cv Lalat. Single application of the herbicide bensulfuron methyl or pretilachlor resulted in a significant reduction of N₂O and CH₄ emissions while the combination of these two herbicides distinctly increased N₂O and CH₄ emissions. Cumulative N₂O emissions (kg N₂O-N) followed the order of bensulfuron methyl (0.35 kg ha⁻¹) < pretilachlor (0.36 kg ha⁻¹) < control (0.45 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (0.49 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (0.54 kg ha⁻¹). Cumulative CH₄ emissions (kg CH₄), on the other hand, followed the order of bensulfuron methyl (47.89 kg ha⁻¹) < pretilachlor (73.17 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% single dose (93.50 kg ha⁻¹) < control (106.54 kg ha⁻¹) < bensulfuron methyl 0.6% + pretilachlor 6.0% double dose (124.67 kg ha⁻¹). The inhibitory effect of separate application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% on N₂O emission was linked to lower mineral N, lower denitrifying and nitrifying activity and low denitrifier and nitrifier populations. Inhibitory effect on CH₄ emission, on the contrary, was linked to prevention in the drop of redox potential, lower readily mineralizable carbon (RMC) and microbial biomass carbon (MBC) contents as well as lower methanogenic and higher methanotrophic bacterial population. Admittedly, stimulatory effect of combined application of herbicides bensulfuron methyl 0.6% and pretilachlor 6.0% at double dose on N₂O and CH₄ emission was related to reversal of the identified indicators of inhibition. Results indicate that while individual application of herbicides bensulfuron methyl 0.6% or pretilachlor 6.0% can reduce N₂O and CH₄ emission from flooded soil planted to rice, their combined application at normal dose can keep the emission at a comparatively lower level with significantly higher grain yield as compared to the herbicides applied alone.     

金属改性碳脱除PH3和H2S动力学及反应机理研究

为综合利用黄磷尾气中的CO,通过计算平均活化能和测定XPS、TG/DTA和氮吸附特性的方法,研究了Cu²⁺和某金属离子Mn⁺改性碳脱除PH₃和H₂S的动力学和反应机理问题。结果表明：H₂S在金属改性碳上反应时平均活化能为134.4 J/mol为-0.76级反应,PH₃在金属改性碳上反应时平均活化能为1 247.6 J/mol为-0.8级反应;减小改性碳粒径增加流量可以显著提高其脱除PH₃和H₂S的速率;XPS、TG/DTA和孔径分布分析证明,改性碳净化H₂S和PH₃是一个催化吸附过程,H₂S和PH₃首先与氧在改性碳表面进行催化氧化反应,然后生成S和P₂O₅沉积吸附在改性碳表面。     

Estimates of synthetic fertilizer N-induced direct nitrous oxide emission from Chinese croplands during 1980-2000

There is increasing concern that agricultural intensification in China has greatly increased N₂O emissions due to rapidly increased fertilizer use. By linking a spatial database of precipitation, synthetic fertilizer N input, cropping rotation and area via GIS, a precipitation-rectified emission factor of N₂O for upland croplands and water regime-specific emission factors for irrigated rice paddies were adopted to estimate annual synthetic fertilizer N-induced direct N₂O emissions (FIE-N₂O) from Chinese croplands during 1980-2000. Annual FIE-N₂O was estimated to be 115.7 Gg N₂O-N year⁻¹ in the 1980s and 210.5 Gg N₂O-N year⁻¹ in the 1990s, with an annual increasing rate of 9.14 Gg N₂O-N year⁻¹ over the period 1980-2000. Upland croplands contributed most to the national total of FIE-N₂O, accounting for 79% in 1980 and 92% in 2000. Approximately 65% of the FIE-N₂O emitted in eastern and southern central China.     

Ecotoxicological assessment of TiO2 byproducts on the earthworm Eisenia fetida

The increasing production of nanomaterials will in turn increase the release of nanosized byproducts to the environment. The aim of this study was to evaluate the behaviour, uptake and ecotoxicity of TiO₂ byproducts in the earthworm Eisenia fetida. Worms were exposed to suspensions containing 0.1, 1 and 10 mg/L of byproducts for 24 h. Size of TiO₂ byproducts showed aggregation of particles up to 700 μm with laser diffraction. Only worms exposed at 10 mg/L showed bioaccumulation of titanium (ICP-AES), increasing expression of metallothionein and superoxide dismutase mRNA (Real-time PCR) and induction of apoptotic activity (Apostain and TUNEL). TiO₂ byproducts did not induce cytotoxicity on cœlomocytes, but a significant decrease of phagocytosis was observed starting from 0.1 mg/L. In conclusion, bioaccumulation of byproducts and their production of reactive oxygen species could be responsible for the alteration of the antioxidant system in worms.     

Effects of high atmospheric CO2 concentration on root hydraulic conductivity of conifers depend on species identity and inorganic nitrogen source

We examined root hydraulic conductivity (L_p) responses of one-year-old seedlings of four conifers to the combined effects of elevated CO₂ and inorganic nitrogen (N) sources. We found marked interspecific differences in L_p responses to high CO₂ ranging from a 37% increase in P. abies to a 27% decrease in P. menziesii, but these effects depended on N source. The results indicate that CO₂ effects on root water transport may be coupled to leaf area responses under nitrate (NO₃⁻), but not ammonium (NH₄⁺) dominated soils. To our knowledge, this is the first study that highlights the role of inorganic N source and species identity as critical factors that determine plant hydraulic responses to rising atmospheric CO₂ levels. The results have important implications for understanding root biology in a changing climate and for models designed to predict feedbacks between rising atmospheric CO₂, N deposition, and ecohydrology.     

Sensitivity analysis for models of greenhouse gas emissions at farm level. Case study of N(2)O emissions simulated by the CERES-EGC model

Modelling complex systems such as farms often requires quantification of a large number of input factors. Sensitivity analyses are useful to reduce the number of input factors that are required to be measured or estimated accurately. Three methods of sensitivity analysis (the Morris method, the rank regression and correlation method and the Extended Fourier Amplitude Sensitivity Test method) were compared in the case of the CERES-EGC model applied to crops of a dairy farm. The qualitative Morris method provided a screening of the input factors. The two other quantitative methods were used to investigate more thoroughly the effects of input factors on output variables. Despite differences in terms of concepts and assumptions, the three methods provided similar results. Among the 44 factors under study, N₂O emissions were mainly sensitive to the fraction of N₂O emitted during denitrification, the maximum rate of nitrification, the soil bulk density and the cropland area.     

Ethylenediurea (EDU): a research tool for assessment and verification of the effects of ground level ozone on plants under natural conditions

Ethylenediurea (EDU) has been widely used to prevent ozone (O₃) injury and crop losses in crop plants and growth reductions in forest trees. Successful use requires establishing a dose/response curve for EDU and the proposed plant in the absence of O₃ and in the presence of O₃ before initiating multiple applications to prevent O₃ injury. EDU can be used to verify foliar O₃ symptoms in the field, and to screen plants for sensitivity to O₃ under ambient conditions. Despite considerable research, the mode of action of EDU remains elusive. Additional research on the mode of action of EDU in suppressing O₃ injury in plants may also be helpful in understanding the mode of action of O₃ in causing injury in plants.     

Combined effects of elevated CO2 and natural climatic variation on leaf spot diseases of redbud and sweetgum trees

Atmospheric CO₂ concentrations are predicted to double within the next century and alter climate regimes, yet the extent that these changes will affect plant diseases remains unclear. In this study conducted over five years, we assessed how elevated CO₂ and interannual climatic variability affect Cercospora leaf spot diseases of two deciduous trees. Climatic data varied considerably between the five years and altered disease expression. Disease incidence and severity for both species were greater in years with above average rainfall. In years with above average temperatures, disease incidence for Liquidambar styraciflua was decreased significantly. When significant changes did occur, disease incidence and severity always increased under elevated CO₂. Chlorophyll fluorescence imaging of leaves revealed that any visible increase in disease severity induced by elevated CO₂ was mitigated by higher photosynthetic efficiency in the remaining undamaged leaf tissue and in a halo surrounding lesions.     

Subacute effects of a phosphorothionate pesticide on mixed function oxidases of wistar rats

Abstract

Subacute oral toxicity of a newly developed phosphorothionate insecticide (2‐butenoic acid‐3‐(diethoxy‐phosphinothioyl) methyl ester), coded as RPR‐2, was studied in male rats by oral (multiple) intubation of low (0.014 mg kg^‐1 day^‐1), medium (0.028 mg kg^‐1 day^‐1), and high (0.042 mg kg^‐1 day^‐1) dose for 90 days. The medium and high dose produced toxic symptoms along‐with some mortality (20%) occurred in the high dose treated rats. The medium and high doses caused significant inhibition in cytochrome P‐450 activity in liver, lung, kidney and brain tissues at 45 and 90 days. The high dose caused significant decrease in cyt.b₅ activity of all the four tissues at 45 and 90 days. Whereas, medium dose brought such effect in liver and lung at 45 and 90 days. Kidney and brain cyt.b₅ activity decreased significantly at 90^th day due to medium dose. Low dose also caused inhibition in cyt.b₅ activity in brain at 90^th day. Cytochrome P‐450 reductase activity was decreased significantly in liver, lung, kidney and brain at 45 and 90^th by the medium and high dose. The results indicated that RPR‐2 had potential to modulate hepatic and extra‐hepatic cyt.P‐450 dependent monooxygenase system of rat due to subacute exposure. These metabolic alterations were quite reversible after 28 days withdrawal of treatment.